Containers for aerosol formulations commonly comprise a vial body coupled to a valve. The valve comprises a valve stem through which the formulation is dispensed. Generally the valve includes a rubber valve seal intended to allow reciprocal movement of the valve stem while preventing leakage of propellant from the container.
It has been found that in some conventional devices the valve stem may tend to stick, pause, or drag during the actuation cycle with the result that the user may perceive a ‘notchiness’ as the valve stem is depressed and released. This may be partly caused by the drug sedimenting or precipitating out of the drug-propellant suspension or solution formulation and depositing on the internal valve components, the presence of drug on the sliding interface creating increased friction during operation.
Prior art seals generally comprise a rubber ring formed by stamping out a ring shape from a sheet of rubber material. The ring aperture, thus, inevitably has square-cut edges which present a relatively high area of contact between the seal and the stem. Furthermore, when the valve stem is moved in such square-cut seals the seal deforms in such a way that the surface area, and hence the frictional contact area, between the seal and stem increases.
The Applicants have now found that the above described problem of notchiness may be ameliorated without compromising sealing performance if the valve seal consists of two components: a rigid component and a flexible component. The two components may be arranged so that there is a rigid outer section and a flexible inner section. The flexible section allows for movement of the seal against the stem, while the rigid outer section reduces deformation of the seal and therefore keeps the increase in surface area, and hence frictional contact area, to a minimum. The two components may also be arranged in other suitable ways.
The increase in surface area may be further reduced by shaping the seal so as to reduce the area of contact between the seal and the stem. Cutting one or more grooves or small channels in the non stem-receiving surfaces of the sealing ring provides space for the stem-receiving part of the sealing ring to move into upon movement of the valve stem, resulting in reduced deformation and friction at the contact surface with the valve stem.
A further problem with prior art seals arises due to ingress and absorption of propellant (e.g. HFA 134a) and moisture by the rubber seal. The presence of the propellant or moisture in the rubber can lead to swelling of the rubber material and consequently a reduction in the performance of the seal. The use of a two component valve seal can reduce the amount of swelling occurring if one component is composed of material more resistant to propellant and moisture, thereby decreasing the amount of propellant or moisture absorbing material present in the seal.